325 



matter which could be read in the microscope could not be read 

 with Beale's neutral tint ; moreover, it cannot be read what- 

 ever way you place the slide, so long as the cover glass is to- 

 wards the objective. In order to read it with Beale's neutral 

 tint the slide must be placed on the stage with the cover glass 

 down and the slip next the objective. It behoves, therefore, 

 every microscopist who makes drawings to bear this important 

 fact in mind. 



Mr. Karop exhibited some -ph.otogrs.'phs oi Amphipletira, which 

 he thought deserved notice, and read a translation of a paper " On 

 the resolution of Amphipleura pellucida by violet filtered light." 



Mr. C. L. Curties inquired what condenser was used to show 

 the lines as they appeared in the photograph. 



Mr. Karop said that the firm of Zeiss had lent for the purpose 

 one of their achromatic condensers of l"6 N.A, the same as that 

 of the lens. 



The President said the resolution of the longitudinal striae in 

 Amphipleura was a much vexed question, because lines could be 

 made to run over the object by using oblique light, and a photo- 

 gTaf)h might in that way show them whether they were there 

 or not. For his own part he should not believe in them until 

 he had seen their spectra at the back of the objective. 



Mr. Newton said that understanding it was the violet and 

 blue rays which chiefly affected the photographic plate, and 

 supposing they used ordinary light, would they not be apt to 

 focus for the red and the yellow rather than for the violet and 

 blue ; whereas if monochromatic light were used could they not 

 focus for blue with much greater certainty ? 



The President said that the apochromatic lens would save the 

 trouble, because the rays were all brought to the same point, 

 but the old lenses would need the light filter. 



The thanks of the Club were voted to Mr. Karop for his 

 translation of the paper. 



The President said that there was in the last Journal a com- 

 munication from Mr. Ashe describing a plan for estimating tube 

 lengths. Since then he had sent them another paper, giving a 

 much simpler method of doing the same thing. 



Mr. Ashe then read his paper on the subject, drawing figures 

 upon the black-board to illustrate the points dealt with. He 

 thought it would be found a useful means of analysis as enabling 

 them to determine how much of the magnifying power was due 



